1. Field of the Invention
This invention relates to a security document with a security element having at least a first layer with gaps in the form of characters or patterns, and a magnetic layer disposed below said first layer. The invention relates further to such a security element and to methods for producing said element and the document.
2. Discussion of Related Technology
It has been known for some time to provide security documents with plastic security threads having a magnetic coating and thus serving as a machine-readable security feature (DE 16 96 245 A1, EP 0 310 707 A1).
To increase the forgery-proofness of this proven security feature further, it has also been proposed to provide the magnetic coating on the carrier material in discontinuous form. For example EP 0 407 550 A1 describes a security document with an embedded security thread provided with a binary code consisting of magnetic material. Certain bit lengths are defined which are constant over the total length of the strip. The coating of a bit length with magnetic material corresponds for example to a 1 while a bit length without magnetic material corresponds to a 0. The binary code known from EP 0 407 550 A1 is characterized in that it is composed of alternatingly disposed separation segments and word segments whereby the word portion consists of a certain number of bit lengths and the sequence of binary values of the separation segments must not occur within this word length in order to permit clear detection of the word segments.
This security element has the disadvantage, however, that there is no possibility of fast visual checking as is necessary in many situations of daily life.
It has therefore likewise been proposed to combine machine-testable security features with visual features. EP 0 516 790 A1 discloses a security document with such a security element. The security thread described here consists of a transparent plastic carrier layer with a metallic coating in which gaps are provided in the form of characters or patterns, the so-called negative writing. If the thread is present in the paper pulp, these gaps and the metallic surroundings are hardly visible when viewed by reflected light. When viewed by transmitted light, however, the transparent gaps stand out in strong contrast from their opaque surroundings and are thus easily recognized. At the same time the security element has a magnetic coating which can e.g. be disposed congruently below the metal layer so that the gaps are present congruently in both layers. In this case a transparent plastic foil is first printed in the area of the later gaps with an activable ink containing foamable additives for example. Subsequently the plastic foil is provided in consecutive working steps first with a first metal layer, a magnetic layer and a second metal layer. Subsequent activation of the ink, e.g. thermal action, causes the layers to be removed in the area of the activable ink so that the gads arise.
Alternatively the magnetic coating can be provided below the metal layer only in the edge areas of the thread and along the running direction of the element in the document, the gaps being disposed in the metal layer in the intermediate areas free from the magnetic layer. The transparent carrier foil of the thread is printed in the edge areas with magnetic material in the form of strips. In the intermediate areas free from the magnetic layer the activable ink is applied in the form of the later gaps and the carrier foil then coated all over with the metal layer. The following activation of the ink finally gives rise to the gaps in the metal layer.
The invention is based on the problem of proposing a security document with a security element which allows not only a visual check but also machine testing and offers increased protection from forgery.
The solution to a problem can be seen in the independent claims. Developments are the object of the subclaims.
Hitherto it was impossible to combine a visual feature testable in transmission, such as the negative writing, with a magnetic coding usually consisting of spaced, opaque, magnetic areas. If the coding and the negative writing are provided on the security element independently of each other, there is a danger of the opaque areas of the coding extending into the negative characters or even covering them completely so that the characters are hardly or not at all recognizable in transmission. On the other hand, if one also provides the gaps in the magnetic layer in the overlap areas between magnetic layer and negative characters one can no longer distinguish without doubt between the actual coding and the superimposed characters when reading the coding.
The invention is based on the finding that the extension of the negative characters is in the micron range and therefore a suitable choice of the extension of the magnetic areas and of the material parameters of the magnetic substance influencing the magnetic flux will prevent the readability of the coding from being impaired by the superimposed negative characters.
According to the invention a discontinuous magnetic layer in the form of a coding is therefore provided below the opaque layer surrounding the negative characters, the gaps also being present in the magnetic layer in the areas where the negative character gaps and the magnetic layer overlap.
According to a preferred embodiment the security document has a security element with a translucent or transparent plastic layer on which a magnetic binary coding with a bit length of at least 2 to 4 mm and an opaque metal layer with negative characters are disposed, the metal layer being provided over the coding. In the areas where the negative characters overlap the magnetic layer the magnetic layer also has gaps in the form of the characters. Under the magnetic layer one can likewise dispose, for additional visual protection of the coding, a metal layer, e.g. of aluminum or metallic ink, which likewise has the negative character gaps. The magnetic material and quantitative parameters are selected such that the magnetic flux is roughly twice as high as would be necessary for reading the coding on an uninterrupted thread.
The inventive security element is produced in principle in two steps, in one case producing the magnetic coding and in the other case producing the negative writing. In the following the various possibilities for producing a magnetic coding and visually recognizable negative writing will therefore first be explained independently of each other.
Since a magnetic layer is preferably covered by an essentially opaque protective layer on both sides for protection from forgery, the method variants described in the following include not only the production of the magnetic coding itself but also the possibilities for producing a magnetic coding with a subjacent cover layer. This is preferably a metallic layer which can be produced by any method, such as vacuum metalization, printing with bronze inks or the like. However other layers are of course also conceivable, such as a white color layer. One can also use color layers containing iridescent or liquid-crystal pigments or other optically variable effect layers, such as holograms. Semitransparent layers such as a semitransparent metal layer are likewise conceivable.
Production Variant M1 (for Producing a Magnetic Coding)
The inverse of the desired magnetic coding is printed on a carrier foil with an activable ink as a separation layer. Subsequently the lower cover layer and the magnetic layer are applied all over and uniformly distributed. The separation layer is then activated, e.g. by treatment with a suitable solvent. The dissolving process can possibly be supported by surfactants, ultrasound or mechanical brushing. This causes the separation layer and the superjacent layers to be removed. The magnetic coding remains on the foil.
Production Variant M2 (for Producing a Magnetic Coding)
A continuous lower cover layer is first applied to a carrier foil. The inverse of the magnetic coding is printed thereon with an activable ink as a separation layer. Subsequently the magnetic layer is applied all over and uniformly distributed. In the next operation the separation layer is activated, for example likewise by treatment with a suitable solvent. This process can possibly be supported by surfactants, ultrasound or mechanical brushing. In this way the layers are removed in the area of the separation layer and the magnetic coding remains. However, the lower cover layer is present all over.
Production Variant M3 (for Producing a Magnetic Coding)
The magnetic layer is printed in the desired coding directly on a carrier foil or transferred in the desired coding thereto using a transfer method. The carrier foil can optionally have a cover layer.
Production Variant M4 (for Producing a Magnetic Coding)
The magnetic layer is applied all over to a carrier foil already provided all over with the lower cover layer. Subsequently the pattern of the coding is printed with a strongly adhesive ink. In a further step the magnetic layer is detached in the unprinted areas, possibly supported by ultrasound or mechanical brushing. The protective and strongly adhesive ink layer can optionally be detached subsequently.
Production Variant M5 (for Producing a Magnetic Coding)
The magnetic layer is applied all over to a carrier layer already provided with the lower cover layer. Subsequently the inverse of the magnetic coding is printed with a caustic ink containing e.g. an acid, solvent or completing agent. This causes the unwanted parts of the magnetic layer to be detached and the magnetic coding to remain. The detaching process can again be supported by surfactants, ultrasound or mechanical brushing.
The opaque or at least partly opaque layer having the negative characters can, like the abovementioned first cover layer, consist of a metal layer, an opaque ink, a bronze ink, a hologram or the like. The term xe2x80x9copaque layerxe2x80x9d used in the following also includes essentially opaque layers, such as semitransparent metal layers or inks with optically variable pigments such as interference layer pigments or liquid-crystal pigments. For producing the light, visually easily recognized characters against an opaque background one can fundamentally use the following possible methods.
Production Variant V1 (for Producing Gaps)
A translucent carrier foil is printed in the form of the later characters using a soluble ink as a separation layer. This layer structure is subsequently provided with the opaque layer. Then the separation layer is detached with a suitable solvent, which leads to detachment of the superjacent layer.
Production Variant V2 (for Producing Gaps)
A carrier foil is provided with at least one opaque layer by printing or vaporization. Then a strongly adhesive, translucent ink is printed on the uppermost cover layer in the form of the inverse of the later gaps, and the non-covered areas subsequently removed by being etched off or dissolved.
Production Variant V3 (for Producing Gaps)
A carrier foil is printed with an opaque ink containing for example bronze powders, white titanium dioxide pigments or optically variable pigments, the negative characters being left out.
Production Variant V4 (for Producing Gaps)
A carrier foil is printed or vaporized with at least one opaque layer. Then a caustic ink containing for example an acid, solvent or complexing agent is applied to the sequence of layers in the form of the later gaps so that the subjacent layers are removed except for the carrier foil.
These separately specified methods for producing a magnetic coding and negative writing can be combined at will in order to obtain an inventive security element or security document. A carrier foil, preferably in endless form, is provided both with the magnetic coding and with the superjacent negative writing. Subsequently this carrier foil is cut into security elements with the desired form, preferably strips or bands. In a last step this security element is connected with the security document material. The element can be for example embedded in the document material as a security thread or fastened all over to the document surface. The carrier foil can also act merely as an intermediate carrier, i.e. the layer structure consisting of negative writing and magnetic coding is transferred to the document by means of an adhesive or lacquer and the carrier foil then removed. In this case one must sure the order is right when producing the layers on the intermediate carrier so that the magnetic coding comes to lie under the negative writing on the document.